Khartoum, 16 May-(ANA)-Sudan has accused Chad of carrying out air raids inside its territory, and said it was assessing how to respond.
One Sudanese official described the alleged raids as an act of war and said there had been casualties - though another official said no-one was hurt.
The accusation comes 10 days after Chad said Sudan had backed Chadian rebels.
The two states have long traded accusations of supporting rebels in each other's territory, especially around Sudan's war-torn Darfur area.
Chadian communications Minister Mahamat Hissene was quoted by AFP news agency on Friday as saying he was "surprised to learn that the regime in Khartoum is protesting against a Chadian air force action: this is obviously the pot calling the kettle black".
He was also quoted by AP news agency as saying he would "wouldn't be surprised" if there were raids since the Chadian military had been chasing rebels out of the country.
Earlier, Sudanese foreign ministry spokesman Ali Sadiq said two Chadian aeroplanes had carried out strikes on areas 60km (40 miles) inside Sudan.
The raids had taken place in deserted areas and there were no casualties, he was quoted as saying by AFP.
But Ali Youssef Ahmed, head of protocol at Sudan's foreign ministry, was quoted by Reuters news agency as saying: "They attacked. They bombed and there were casualties."
The Chadian planes crossed the border just south of Geneina, Darfur, he said.
He said that three, rather than two, planes had been involved.
Sudan has summoned the Chadian ambassador and alerted the UN Security Council, the Arab League and the African Union, a statement from Mr Sadiq said.
"The Sudanese army is ready to respond but is waiting for instructions from the leadership," he said.
Last week Chad's government said it had repelled a rebel "invasion" from Sudan, and accused Khartoum of backing the rebel forces.
That accusation came two days after Chad and Sudan had signed a reconciliation agreement in Qatar.
Officials in Chad said 220 rebels were killed and 120 captured.
Rebels have been trying to topple Chadian President Idriss Deby for more than three years.
Although Khartoum has repeatedly denied backing the rebels, analysts note the insurgents have operated out of Sudanese territory for several years.
Sudan has also long accused Chad of supporting rebels in the western Sudanese region of Darfur.
In May 2008, Khartoum accused N'Djamena of backing Darfur-based insurgents who launched an unprecedented attack on the Sudanese capital.
Many Darfur rebels are from the same ethnic group as Mr Deby, and ever since their uprising began, he has been accused of offering them support. (ANA)
